The primary purpose of this project is to develop a serum-free medium suitable for the growth of primary and early passage SHE cells. Availability of such a medium will facilitate standardization of geneotoxic testing protocols and studies on mechanisms of carcinogenesis, both significant areas relevant to regulatory considerations and the public health. Phase I studies involve: (a) Selection of a suitable basal medium by clonal titration of different serum lots in two or more candidate basal media. (b) Substitution of growth factors and hormones for serum. Optimization of components and concentrations by clonal titration. (c) Determine clonal growth response of SHE cells in serum-free medium. (d) Assay for transforming growth factor secretion by SHE cells in serum- free medium by induction of anchorage independent growth of NRK cells, and identification of individual TGF-beta 1 and TGF-beta 2. (SHE = Syrian Hamster Embryo)